1. Field of the Invention
The present invention relates to a roller bearing for a linear motion which is low in terms of the friction and has high accuracy and high rigidity and which may be applied to a linear motion part of a machine which is required to possess high operation performance and high accuracy, such as a machine tool, an industrial machine or a measuring apparatus.
2. Description of the Prior Art
A roller bearing for a linear motion has heretofore been known, such as that shown in FIGS. 13 and 14. More specifically, a roller bearing 1 is composed of a bearing body 4, a pair of end caps 6, 6, a multiplicity of rollers 7, 7 . . . and a guide member 9. The bearing body 4 has a substantially H-shaped cross-section and upper and lower surfaces opposing each other. A non-loaded roller rolling passage which is constituted by a single non-loaded roller rolling groove 2 with a rectangular cross-section is formed on the upper surface of the bearing body 4, while a loaded roller rolling passage which is constituted by a single loaded roller rolling groove 3 is formed on the lower surface. The end caps 6, 6 are respectively secured to both longitudinal ends of the bearing body 4. Each of the end caps 6, 6 is provided therein with a circular roller turning passage 5 which connects the non-loaded and loaded roller rolling grooves 2 and 3. The rollers 7, 7 . . . are housed within the non-loaded and loaded roller rolling grooves 2 and 3. Each of the rollers 7, 7 . . . is constituted by two cylindrical members which are coaxially connected together by a smaller-diameter connecting portion 7a. The guide member 9 is constituted by an endless wire which is disposed such as to surround the connecting portions 7a, 7a . . . of all the rollers 7, 7 . . . and to thereby guide and retain the rollers 7, 7 . . .
Incidentally, when the above-described roller bearing 1 is applied to a linear motion part of various kinds of machine, the following problem is encountered. Namely, the loaded rollers 7, 7 . . . , being disposed within the loaded roller rolling groove 3 of the bearing body 4, roll on the slide surface (not shown) of the machine, and when doing so, the load applied to the loaded rollers 7, 7 . . . from the slide surface is born by side portions 8, 8 of the bearing body 4, which has a substantially H-shaped cross-section, on both sides of the roller rolling grooves 2, 3. In consequence, the bearing body 4 may be warped at its central portion which has a lesser thickness than its side portions and consequently has smaller rigidity. As a result, an abnormally large surface pressure may act on both end portions 7b, 7b of each of the loaded rollers 7, causing the rollers 7 to become abnormally worn and the life of the roller bearing 1 to be unfavorably shortened.
Further, since the loaded rollers 7, 7 . . . are retained solely by a single guide member 9 constituted by an endless wire, the rollers 7, 7 . . . easily skew as they enter the loaded region (loaded roller rolling groove) from the non-loaded region, so that there is a risk of breakage of the smaller-diameter connecting portions 7a, 7a . . . respectively constituting the central portions of the rollers 7, 7 . . .
Still another problem experienced with the conventional roller bearing 1 is that when the side surfaces of an annular groove formed in the center of each of the rollers 7, 7 . . . within the loaded region contacts any curved portion of the guide member 9, the rollers 7, 7 encounter large resistance and they are thereby prevented from rolling smoothly.